Study of the efficiency of event start time determination at BESⅢ

A method to estimate the efficiency of event start time determination at BESIII is developed.This method estimates the efficiency at the event level by combining the efficiencies of various tracks(e,μ,π,K,p,γ)in a Bayesian way.Efficiencies results and the difference between data and MC at the track level are presented in this paper.For a given physics channel,event start time efficiency and systematic error can be estimated following this method.     

Study of the efficiency of event start time determination at BESⅢ

A method to estimate the efficiency of event start time determination at BESⅢ is developed. This method estimates the efficiency at the event level by combining the efficiencies of various tracks (e, μ, π, K, p, γ) in a Bayesian way. Efficiencies results and the difference between data and MC at the track level are presented in this paper. For a given physics channel, event start time efficiency and systematic error can be estimated following this method.     

Prototype of time digitizing system for BESⅢ endcap TOF upgrade

The prototype of a time digitizing system for the BESⅢ endcap TOF (ETOF) upgrade is introduced in this paper. The ETOF readout electronics has a distributed architecture. Hit signals from the multi-gap resistive plate chamber (MRPC) are signaled as LVDS by front-end electronics (FEE) and are then sent to the back-end time digitizing system via long shield differential twisted pair cables. The ETOF digitizing system consists of two VME crates, each of which contains modules for time digitization, clock, trigger, fast control, etc. The time digitizing module (TDIG) of this prototype can support up to 72 electrical channels for hit information measurement. The fast control (FCTL) module can operate in barrel or endcap mode. The barrel FCTL fans out fast control signals from the trigger system to the endcap FCTLs, merges data from the endcaps and then transfers to the trigger system. Without modifying the barrel TOF (BTOF) structure, this time digitizing architecture benefits from improved ETOF performance without degrading the BTOF performance. Lab experiments show that the time resolution of this digitizing system can be lower than 20 ps, and the data throughput to the DAQ can be about 92 Mbps. Beam experiments show that the total time resolution can be lower than 45 ps.     

Time calibration for the end cap TOF system of BESⅢ

The time calibration for end cap TOF system of BESⅢ is studied in this paper. It has achieved about 110 ps time resolution for muons in dimu events. The pulse height correction using electronic scan curve and the predicted time calculated using Kalman filter method are introduced. This paper also describes the study of using electrons and muons as calibration samples.     

Study of the online event filtering algorithm for BESⅢ

The results of a study of event tagging strategies for elementary physics processes in the τ-charm region are presented. The algorithm for online event filtering is optimized by adopting the information provided by different sub-detectors according to their strengths and capacities. The algorithm is tested with various generated physics and background events. The results indicate that the algorithm satisfies the requirements of BESⅢ physics analysis and its     

Event generators at BESⅢ

We present a brief remark and introduction to event generators for tau-charm physics currently used at BESⅢ, including KKMC, BesEvtGen, Bhlumi, Bhwide, Babayaga and inclusive Monte-Carlo event generators. This paper provides basic information on event generators for BESⅢ users.     

An extended segment pattern dictionary for a pattern matching tracking algorithm at BESⅢ

A pattern matching based tracking algorithm, named MdcPatRec, is used for the reconstruction of charged tracks in the drift chamber of the BES detector. This paper addresses the shortage of segment finding in the MdcPatRec algorithm. An extended segment construction scheme and the corresponding pattern dictionary are presented. Evaluation with Monte-Carlo and experimental data show that the new method can achieve higher efficiency for low transverse momentum tra     

Track reconstruction using the TSF method for the BESⅢ main drift chamber

We describe the algorithm to reconstruct the charged tracks for BESⅢ main drift chamber at BEPCⅡ, including the track finding and fitting. With a new method of the Track Segment Finder (TSF), the results of present study indicate that the algorithm can reconstruct the charged tracks over a wide range of momentum with high efficiency, while improving the robustness against the background noise in the drift chamber. The overall performances, including spatial resolution, momentum resolution and secondary vertices reconstruction efficiency, etc. satisfy the requirements of BESⅢ experiment.     

Determination of the number of ψ' events at BESⅢ

The number of ψ’ events accumulated by the BESⅢ experiment from March 3 through April 14, 2009, is determined by counting inclusive hadronic events. The result is 106.41×(1.00±0.81%)×106 . The error is systematic dominant; the statistical error is negligible.     

Determination of the number of ψ' events at BES Ⅲ

The number of ψ' events accumulated by the BESⅢ experiment from March 3 through April 14, 2009, is determined by counting inclusive hadronic events. The result is 106.41×(1.00±0.81%)×106 . The error is systematic dominant; the statistical error is negligible.     

Fast simulation of the forward tracking detector of HPLUS

The necessity of installing a forward tracking detector stack is discussed for the Hadron Physics LanzhoU Spectrometer(HPLUS). A local tracker is developed to solve the multi-track finding problem. The track candidates are searched iteratively via Hough Transform. The fake tracks are removed by a least square fitting process. With this tracker we have studied the feasibility of     

Determination of the number of ψ(3686)events at BESⅢ

The numbers of ψ(3686) events accumulated by the BESⅢ detector for the data taken during 2009 and2012 are determined to be(107.0±0.8)×10~6 and(341.1±2.1)×10~6, respectively, by counting inclusive hadronic events,where the uncertainties are systematic and the statistical uncertainties are negligible. The number of events for the sample taken in 2009 is consistent with that of the previous measurement. The total number of ψ(3686) events for the two data taking periods is(448.1±2.9)×10~6.     

Calibration of RPC-based muon detector at BESⅢ

The calibration algorithm for RPC-based muon detector at BESIII has been developed. The calibration method, calibration error and algorithm performance are studied. The primary results of efficiency and noise at layer, module and strip levels have been calibrated with cosmic ray data. The calibration constants are available for simulation and reconstruction tuning. The results of Monte Carlo and data are also compared to check the validation and reliability of the algorithm.     

Trigger efficiencies at BESⅢ

Trigger efficiencies at BESⅢ were determined for both the J/ψ and ψ＇ data taking of 2009. Both dedicated runs and physics datasets are used; efficiencies are presented for Bhabha-scattering events, generic hadronic decay events involving charged tracks, dimuon events and ψ＇→π＋π-J/ψ, J/ψ→ 1＋1- events.The efficiencies are found to lie well above 99% for all relevant physics cases, thus fulfilling the BESⅢ design specifications.     

Mini-review of rare charmonium decays at BESⅢ

Recently, the LHCb experiment announced 3.5σ evidence for direct CP violation in D⁰ decay by looking at the difference between A_CP(D⁰→K⁺K^-) and A_CP(D⁰→π⁺π^-). This is the rst evidence of CP violation in a charm system, which may indicate new physics beyond the Standard Model. Motivated by this measurement, we review rare processes in charmonium decay, especially, the weak decay, C or P violated decay, and lepton avor violated decays. In case the new physics appears in charm sector, these rare decays of charmonium states will provide an opportunity to search for signi cant contributions from physics beyond the Standard Model. With huge J/ψ and ψ(2S) samples in BES0 experiment, the rare decays may be feasible.     

Calibration of RPC-based muon detector at BESⅢ

The calibration algorithm for RPC-based muon detector at BESⅢ has been developed. The calibration method, calibration error and algorithm performance are studied. The primary results of efficiency and noise at layer, module and strip levels have been calibrated with cosmic ray data. The calibration constants are available for simulation and reconstruction tuning. The results of Monte Carlo and data are also compared to check the validation and reliability of the algorithm.     

A GEANT4 simulation study of BESⅢ endcap TOF upgrade

A GEANT4-based Monte-Carlo (MC) model is developed to study the performance of endcap time-of-flight (ETOF) at BESⅢ. It's found that the multiple scattering effects, mainly from the materials at the MDC endcap, can cause multi-hit on the ETOF's readout cell and significantly influence the timing property of ETOF. A multi-gap resistive plate chamber (MRPC) with a smaller readout cell structure is more suitable for the ETOF detector due to significantly reduced multi-hit rate (per channel), from 71.5% for currently-used scintillator-based ETOF to 21.8% or 16.7% for MRPC-based ETOF, depending on the readout pad size used. The timing performance of an MRPC ETOF is also improved. These simulation results suggest and guide an ETOF upgrade effort at BESⅢ.     

Significance of absolute energy scale for physics at BESⅢ

The effects of absolute energy calibration on BESⅢ physics are discussed in detail, which mainly involve the effects on τ mass measurement, cross section scan measurement, and generic error determination in other measurements.     

Prototype of time digitizing system for BESⅢ endcap TOF upgrade

The prototype of a time digitizing system for the BESⅢ endcap TOF (ETOF) upgrade is introduced in this paper. The ETOF readout electronics has a distributed architecture. Hit signals from the multi-gap resistive plate chamber (MRPC) are signaled as LVDS by front-end electronics (FEE) and are then sent to the back-end time digitizing system via long shield differential twisted pair cables. The ETOF digitizing system consists of two VME crates, each of which contains modules for time digitization, clock, trigger, fast control, etc. The time digitizing module (TDIG) of this prototype can support up to 72 electrical channels for hit information measurement. The fast control (FCTL) module can operate in barrel or endcap mode. The barrel FCTL fans out fast control signals from the trigger system to the endcap FCTLs, merges data from the endcaps and then transfers to the trigger system. Without modifying the barrel TOF (BTOF) structure, this time digitizing architecture benefits from improved ETOF performance without degrading the BTOF performance. Lab experiments show that the time resolution of this digitizing system can be lower than 20 ps, and the data throughput to the DAQ can be about 92 Mbps. Beam experiments show that the total time resolution can be lower than 45 ps.